RESUMEN
Cardiovascular responses to diving are characterized by two opposing responses: tachycardia resulting from exercise and bradycardia resulting from the apnea. The convergence of bradycardia and tachycardia may determine the cardiovascular responses to diving. The purpose of this study was to investigate the interaction of breath holding and muscle mechanoreflex on cardiovascular responses in breath-hold divers (BHDs) and non-BHDs. We compared the cardiovascular responses to combined apnea and the mechanoreflex in BHDs and non-BHDs. All participants undertook three trials-apnea, passive leg cycling (PLC), and combined trials-for 30 s after rest. Cardiovascular variables were measured continuously. Nine BHD (male:female, 4:5; [means ± SD] age, 35 ± 6 years; height, 168.6 ± 4.6 cm; body mass, 58.4 ± 5.9 kg) and eight non-BHD (male:female, 4:4; [means ± SD] age, 35 ± 7 years; height, 163.9 ± 9.1 cm; body mass, 55.6 ± 7.2 kg) participants were included. Compared to the resting baseline, heart rate (HR) and cardiac output (CO) significantly decreased during the combined trial in the BHD group, while they significantly increased during the combined trials in the non-BHD group (P < 0.05). Changes in the HR and CO were significantly lower in the BHD group than in the non-BHD group in the combined trial (P < 0.05). These results suggest that bradycardia with apnea in BHDs is prioritized over tachycardia with the mechanoreflex, whereas that in non-BHDs is not. This finding implies that diving training changes the interaction between apnea and the mechanoreflex in cardiovascular control.
Asunto(s)
Contencion de la Respiración , Buceo , Frecuencia Cardíaca , Humanos , Masculino , Femenino , Adulto , Buceo/fisiología , Frecuencia Cardíaca/fisiología , Músculo Esquelético/fisiología , Músculo Esquelético/fisiopatología , Apnea/fisiopatología , Reflejo/fisiología , Gasto Cardíaco/fisiología , Reflejo de Inmersión/fisiología , Presión Sanguínea/fisiologíaRESUMEN
Investigation of marine mammal dive-by-dive blood distribution and oxygenation has been limited by a lack of noninvasive technology for use in freely diving animals. Here, we developed a noninvasive near-infrared spectroscopy (NIRS) device to measure relative changes in blood volume and haemoglobin oxygenation continuously in the blubber and brain of voluntarily diving harbour seals. Our results show that seals routinely exhibit preparatory peripheral vasoconstriction accompanied by increased cerebral blood volume approximately 15 s before submersion. These anticipatory adjustments confirm that blood redistribution in seals is under some degree of cognitive control that precedes the mammalian dive response. Seals also routinely increase cerebral oxygenation at a consistent time during each dive, despite a lack of access to ambient air. We suggest that this frequent and reproducible reoxygenation pattern, without access to ambient air, is underpinned by previously unrecognised changes in cerebral drainage. The ability to track blood volume and oxygenation in different tissues using NIRS will facilitate a more accurate understanding of physiological plasticity in diving animals in an increasingly disturbed and exploited environment.
Asunto(s)
Reflejo de Inmersión/fisiología , Buceo/fisiología , Espectroscopía Infrarroja Corta/instrumentación , Animales , Mamíferos/fisiología , Oxígeno/sangre , Oxígeno/metabolismo , Consumo de Oxígeno/fisiología , Phoca/fisiología , Espectroscopía Infrarroja Corta/métodos , Dispositivos Electrónicos VestiblesRESUMEN
OBJECTIVE: To test the hypothesis that death with physiological parallels to human cases of sudden unexpected death in epilepsy (SUDEP) can be induced in seizing rats by ictal activation of oxygen-conserving reflexes (OCRs). METHODS: Urethane-anesthetized female Long-Evans rats were implanted with electrodes for electrocardiography (ECG), electrocorticography (ECoG), and respiratory thermocouple; venous and arterial cannulas; and a laryngoscope guide and cannula or nasal cannula for activation of the laryngeal chemoreflex (LCR) or mammalian diving reflex (MDR), respectively. Kainic acid injection, either systemic or into the ventral hippocampus, induced prolonged acute seizures. RESULTS: Reflex challenges during seizures caused sudden death in 18 of 20 rats-all MDR rats (10) and all but two LCR rats (8) failed to recover from ictal activation of OCRs and died within minutes of the reflexes. By comparison, 4 of 4 control (ie, nonseizing) rats recovered from 64 induced diving reflexes (16 per rat), and 4 of 4 controls recovered from 64 induced chemoreflexes (16 per rat). Multiple measures were consistent with reports of human SUDEP. Terminal central apnea preceded terminal asystole in all cases. Heart and respiratory rate fluctuations that paralleled those seen in human SUDEP occurred during OCR-induced sudden death, and mean arterial pressure (MAP) was predictive of death, showing a 17 or 15 mm Hg drop (MDR and LCR, respectively) in the 20 s window centered on the time of brain death. OCR activation was never fatal in nonseizing rats. SIGNIFICANCE: These results present a method of inducing sudden death in two seizure models that show pathophysiology consistent with that observed in human cases of SUDEP. This proposed mechanism directly informs previous findings by our group and others in the field; provides a repeatable, inducible animal model for the study of sudden death; and offers a potential explanation for observations made in cases of human SUDEP.
Asunto(s)
Reflejo/fisiología , Convulsiones/fisiopatología , Muerte Súbita e Inesperada en la Epilepsia/etiología , Animales , Reflejo de Inmersión/fisiología , Electrocardiografía , Electrodos Implantados , Electroencefalografía , Electrooculografía , Femenino , Frecuencia Cardíaca , Oxígeno/metabolismo , Consumo de Oxígeno/fisiología , Ratas , Ratas Long-Evans , Frecuencia RespiratoriaRESUMEN
The spread of epileptic seizure activity to brainstem respiratory and autonomic regions can elicit episodes of obstructive apnea and of central apnea with significant oxygen desaturation and bradycardia. Previously, we argued that central apneic events were not consequences of respiratory or autonomic activity failure, but rather an active brainstem behavior equivalent to the diving response resulting from seizure spread. To test the similarities of spontaneous seizure-associated central apneic episodes to evoked diving responses, we used nasopharyngeal irrigation with either cold water or mist for 10 or 60â¯s to elicit the diving response in urethane-anesthetized animals with or without kainic acid-induced seizure activity. Diving responses included larger cardiovascular changes during mist stimuli than during water stimuli. Apneic responses lasted longer than 10â¯s in response to 10â¯s stimuli or about 40â¯s in response to 60â¯s stimuli, and outlasted bradycardia. Repeated 10â¯s mist applications led to an uncoupling of the apneic episodes (which always occurred) from the bradycardia (which became less pronounced with repetition). These uncoupled events matched the features of observed spontaneous seizure-associated central apneic episodes. The duration of spontaneous central apneic episodes correlated with their frequency, i.e. longer events occurred when there were more events. Based on our ability to replicate the properties of seizure-associated central apneic events with evoked diving responses during seizure activity, we conclude that seizure-associated central apnea and the diving response share a common neural basis and may reflect an attempt by brainstem networks to protect core physiology during seizure activity.
Asunto(s)
Reflejo de Inmersión/fisiología , Convulsiones/complicaciones , Apnea Central del Sueño/etiología , Apnea Central del Sueño/fisiopatología , Animales , Fenómenos Fisiológicos Cardiovasculares , Masculino , Ratas , Ratas Sprague-DawleyRESUMEN
Respiratory derangements, including irregular, tachypnic breathing and central or obstructive apnea can be consequences of seizure activity in epilepsy patients and animal models. Periods of seizure-associated central apnea, defined as periods >1s with rapid onset and offset of no airflow during plethysmography, suggest that seizures spread to brainstem respiratory regions to disrupt breathing. We sought to characterize seizure-associated central apneic episodes as an indicator of seizure impact on the respiratory rhythm in rats anesthetized with urethane and given parenteral kainic acid to induce recurring seizures. We measured central apneic period onsets and offsets to determine if onset-offset relations were a consequence of 1) a reset of the respiratory rhythm, 2) a transient pausing of the respiratory rhythm, resuming from the pause point at the end of the apneic period, 3) a transient suppression of respiratory behavior with apnea offset predicted by a continuation of the breathing pattern preceding apnea, or 4) a random re-entry into the respiratory cycle. Animals were monitored with continuous ECG, EEG, and plethysmography. One hundred ninety central apnea episodes (1.04 to 36.18s, mean: 3.2±3.7s) were recorded during seizure activity from 7 rats with multiple apneic episodes. The majority of apneic period onsets occurred during expiration (125/161 apneic episodes, 78%). In either expiration or inspiration, apneic onsets tended to occur late in the cycle, i.e. between the time of the peak and end of expiration (82/125, 66%) or inspiration (34/36, 94%). Apneic period offsets were more uniformly distributed between early and late expiration (27%, 34%) and inspiration (16%, 23%). Differences between the respiratory phase at the onset of apnea and the corresponding offset phase varied widely, even within individual animals. Each central apneic episode was associated with a high frequency event in EEG or ECG records at onset. High frequency events that were not associated with flatline plethysmographs revealed a constant plethysmograph pattern within each animal, suggesting a clear reset of the respiratory rhythm. The respiratory rhythm became highly variable after about 1s, however, accounting for the unpredictability of the offset phase. The dissociation of respiratory rhythm reset from the cessation of airflow also suggested that central apneic periods involved activation of brainstem regions serving the diving reflex to eliminate the expression of respiratory movements. This conclusion was supported by the decreased heart rate as a function of apnea duration. We conclude that seizure-associated central apnea episodes are associated with 1) a reset of the respiratory rhythm, and 2) activation of brainstem regions serving the diving reflex to suppress respiratory behavior. The significance of these conclusions is that these details of seizure impact on brainstem circuitry represent metrics for assessing seizure spread and potentially subclassifying seizure patterns.
Asunto(s)
Reflejo de Inmersión/fisiología , Respiración , Convulsiones/fisiopatología , Animales , Encéfalo/fisiopatología , Modelos Animales de Enfermedad , Electrocardiografía , Electroencefalografía , Frecuencia Cardíaca/fisiología , Ácido Kaínico , Masculino , Pletismografía , Ratas Sprague-Dawley , Apnea Central del SueñoRESUMEN
The purpose of this study was to investigate the genetic mechanisms of the defense vascular reactions in response to the diving reflex in humans with polymorphisms in the genes ADBR2, ACE, AGTR1, BDKRB2, and REN We hypothesized that protective vascular reactions, in response to the diving reflex, are genetically determined and are distinguished in humans with gene polymorphisms of the renin-angiotensin and kinin-bradykinin system. A total of 80 subjects (19 ± 1.4 yr) participated in the study. The intensity of the vascular response was estimated using photoplethysmogram. The I/D polymorphism (rs4340) of ACE was analyzed by PCR. REN (G/A, rs2368564), AGTR1 (A/C, rs5186), BDKRB2 (T/C, rs1799722), and ADBR2 (A/G, rs1042713) polymorphisms were examined using the two-step multiplex PCR followed by carrying allele hybridization on the biochip. Subjects with the BDKRB2 (C/C), ACE (D/D), and ADBR2 (G/G, G/A) genotypes exhibited the strongest peripheral vasoconstriction in response to diving. In subjects with a combination of the BDKRB2 (C/C) plus ACE (D/D) genotypes, we observed the lowest pulse wave amplitude and pulse transit time values and the highest arterial blood pressure during face immersion compared with the heterozygous individuals, suggesting that these subjects are more susceptible to diving hypoxia. This study observed that humans with gene polymorphisms of the renin-angiotensin and kinin-bradykinin systems demonstrate various expressions of protective vascular reactions in response to the diving reflex. The obtained results might be used in estimation of resistance to hypoxia of any origin in human beings or in a medical practice.NEW & NOTEWORTHY Our study demonstrates that the vascular reactions in response to the diving reflex are genetically determined and depend on gene polymorphisms of the kinin-bradykinin and the renin-angiotensin systems.
Asunto(s)
Vasos Sanguíneos/fisiología , Reflejo de Inmersión/genética , Reflejo de Inmersión/fisiología , Presión Sanguínea/genética , Presión Sanguínea/fisiología , Bradiquinina/fisiología , Femenino , Homocigoto , Humanos , Hipoxia/genética , Hipoxia/metabolismo , Masculino , Peptidil-Dipeptidasa A/genética , Polimorfismo Genético , Receptor de Angiotensina Tipo 1/genética , Sistema Renina-Angiotensina/fisiología , Vasoconstricción/genética , Vasoconstricción/fisiología , Adulto JovenRESUMEN
PURPOSE: The present study aimed to examine diurnal variation of the diving bradycardia responses on the same day. METHODS: Eighteen young men (age 26 ± 2 years; height 174.2 ± 6.0 cm; body mass 70.2 ± 8.1 kg; body fat 18.0 ± 3.8 %; mean ± standard deviation) participated in this study. Oral temperature, heart rate variability (HRV) from 5-min of electrocardiogram data, and diving bradycardia responses were measured at 0900, 1300, and 1700 hours daily. All participants performed diving reflex tests twice in the sitting position with the face immersed in cold water (1.9-3.1 °C) and apnea at midinspiration for a minimum of 30 s and as long as possible, in consecutive order. RESULTS: Oral temperature was found to be less in the morning (0900) than in the afternoon (1300) and evening (1700). In the frequency domain parameters of heart rate variability, the natural logarithms of high-frequency power were higher in the morning than in the evening. All participants showed bradycardia response to the two diving reflex tests. The peak values of R-R interval during the diving reflex test both for as long as possible and 30 s were longer in the morning than in the afternoon and evening. CONCLUSION: Our results indicated that the maximal bradycardia during the diving reflex test exhibits a diurnal variation, with peak levels at morning and gradual decrease towards the evening. The HRV indexes show the same variation.
Asunto(s)
Bradicardia/fisiopatología , Ritmo Circadiano/fisiología , Reflejo de Inmersión/fisiología , Adulto , Apnea/fisiopatología , Frecuencia Cardíaca/fisiología , Humanos , MasculinoRESUMEN
During underwater submersion, the body responds by conserving O2 and prioritizing blood flow to the brain and heart. These physiological adjustments, which involve the nervous, cardiovascular, and respiratory systems, are known as the diving response and provide an ideal example of integrative physiology. The diving reflex can be stimulated in the practical laboratory setting using breath holding and facial immersion in water. Our undergraduate physiology students complete a laboratory class in which they investigate the effects of stimulating the diving reflex on cardiovascular variables, which are recorded and calculated with a Finapres finger cuff. These variables include heart rate, cardiac output, stroke volume, total peripheral resistance, and arterial pressures (mean, diastolic, and systolic). Components of the diving reflex are stimulated by 1) facial immersion in cold water (15°C), 2) breathing with a snorkel in cold water (15°C), 3) facial immersion in warm water (30°C), and 4) breath holding in air. Statistical analysis of the data generated for each of these four maneuvers allows the students to consider the factors that contribute to the diving response, such as the temperature of the water and the location of the sensory receptors that initiate the response. In addition to providing specific details about the equipment, protocols, and learning outcomes, this report describes how we assess this practical exercise and summarizes some common student misunderstandings of the essential physiological concepts underlying the diving response.
Asunto(s)
Curriculum , Reflejo de Inmersión/fisiología , Frecuencia Cardíaca/fisiología , Fisiología/educación , Mecánica Respiratoria/fisiología , Enseñanza/métodos , Presión Sanguínea/fisiología , Gasto Cardíaco/fisiología , HumanosRESUMEN
AbstractBreath-hold divers are known to develop cardiac autonomic changes and brady-arrthymias during prolonged breath-holding (BH). The effects of BH-induced hypoxemia were investigated upon both cardiac autonomic status and arrhythmogenesis by comparing breath-hold divers (BHDs) to non-divers (NDs). Eighteen participants (9 BHDs, 9 NDs) performed a maximal voluntary BH with face immersion. BHDs were asked to perform an additional BH at water surface to increase the degree of hypoxemia. Beat-to-beat changes in heart rate (HR), short-term fractal scaling exponent (DFAα1), the number of arrhythmic events [premature ventricular contractions (PVCs), premature atrial contractions (PACs)] and peripheral oxygen saturation (SpO2) were recorded during and immediately following BH. The corrected QT-intervals (QTc) were analyzed pre- and post-acute BH. A regression-based model was used to split BH into a normoxic (NX) and a hypoxemic phase (HX). During the HX phase of BH, BHDs showed a progressive decrease in DFAα1 during BH with face immersion (p < 0.01) and BH with whole-body immersion (p < 0.01) whereas NDs did not (p > 0.05). In addition, BHDs had more arrhythmic events during the HX of BH with whole-body immersion when compared to the corresponding NX phase (5.9 ± 6.7 vs 0.4 ± 1.3; p < 0.05; respectively). The number of PVCs was negatively correlated with SpO2 during BH with whole-body immersion (r = -0.72; p < 0.05). The hypoxemic stage of voluntary BH is concomitant with significant cardiac autonomic changes toward a synergistic sympathetic and parasympathetic stimulation. Co-activation led ultimately to increased bradycardic response and cardiac electrophysiological disturbances.
Asunto(s)
Arritmias Cardíacas/etiología , Sistema Nervioso Autónomo/fisiología , Contencion de la Respiración , Buceo/fisiología , Frecuencia Cardíaca/fisiología , Hipoxia/fisiopatología , Adulto , Análisis de Varianza , Complejos Atriales Prematuros/fisiopatología , Reflejo de Inmersión/fisiología , Humanos , Inmersión/fisiopatología , Masculino , Oxígeno/metabolismo , Análisis de Regresión , Complejos Prematuros Ventriculares/fisiopatologíaRESUMEN
BACKGROUND: In patients with long QT syndrome (LQTS), swimming and loud noises have been identified as genotype-specific arrhythmic triggers in LQTS type 1 (LQTS1) and LQTS type 2 (LQTS2), respectively. OBJECTIVE: The purpose of this study was to compare LQTS group responses to arrhythmic triggers. METHODS: LQTS1 and LQTS2 patients were included. Before and after beta-blocker intake, electrocardiograms were recorded as participants (1) were exposed to a loud noise of â¼100 dB; and (2) had their face immersed into cold water. RESULTS: Twenty-three patients (9 LQTS1, 14 LQTS2) participated. In response to noise, LQTS groups showed similarly increased heart rate, but LQTS2 patients had corrected QT interval (Fridericia formula) (QTcF) prolonged significantly more than LQTS1 patients (37 ± 8 ms vs 15 ± 6 ms; P = .02). After intake of beta-blocker, QTcF prolongation in LQTS2 patients was significantly blunted and similar to that of LQTS1 patients (P = .90). In response to simulated diving, LQTS groups experienced a heart rate drop of â¼28 bpm, which shortened QTcF similarly in both groups. After intake of beta-blockers, heart rate dropped to 28 ± 2 bpm in LQTS1 patients and 20 ± 3 bpm in LQTS2, resulting in a slower heart rate in LQTS1 compared with LQTS2 (P = .01). In response, QTcF shortened similarly in LQTS1 and LQTS2 patients (57 ± 9 ms vs 36 ± 7 ms; P = .10). CONCLUSION: When exposed to noise, LQTS2 patients had QTc prolonged significantly more than did LQTS1 patients. Importantly, beta-blockers reduced noise-induced QTc prolongation in LQTS2 patients, thus demonstrating the protective effect of beta-blockers. In response to simulated diving, LQTS groups responded similarly, but a slower heart rate was observed in LQTS1 patients during simulated diving after beta-blocker intake.
Asunto(s)
Antagonistas Adrenérgicos beta/uso terapéutico , Electrocardiografía/efectos de los fármacos , Frecuencia Cardíaca/fisiología , Síndrome de QT Prolongado/fisiopatología , Reflejo/fisiología , Síndrome de Romano-Ward/fisiopatología , Estimulación Acústica/métodos , Adulto , Reflejo de Inmersión/fisiología , Femenino , Frecuencia Cardíaca/efectos de los fármacos , Humanos , Síndrome de QT Prolongado/tratamiento farmacológico , Masculino , Síndrome de Romano-Ward/tratamiento farmacológicoRESUMEN
The diving response is a coordinated physiological response to submersion under water and has been documented amongst all mammals tested to date. The physiological response consists of three primary reflexes: an immediate bradycardia, apnea, and selective constriction of peripheral blood vessels. We hypothesized that mice would exhibit a diving response upon voluntary submersion into water typically seen in other mammals. In this study, telemeters that measure arterial pressure were implanted into male and female C57Bl/6J mice. These mice were trained to voluntarily dive underwater for a distance of 40 cm over a 4-6 s period. Just before the dive, the interbeat interval (IBI) was 87 ± 6 ms (mean ± SD) and diastolic pressure was 99 ± 14 mmHg. Underwater submersion caused (1) a dramatic bradycardia immediately at the onset of each dive, as IBI increased to 458 ± 104 ms, and (2) a large drop in diastolic pressure, to 56 ± 16 mmHg despite the elevation in peripheral resistance. Mice experienced a short bout (~ 2 s) of hypertension (diastolic pressure rose to 131 ± 17 mmHg) upon emergence. The bradycardia and hypotension appeared to be vagally mediated, since both these responses were blocked with atropine pre-treatment. These data demonstrate that the mouse exhibits a robust diving response upon voluntary submersion into water.
Asunto(s)
Presión Arterial/fisiología , Reflejo de Inmersión/fisiología , Frecuencia Cardíaca/fisiología , Ratones Endogámicos C57BL/fisiología , Animales , Femenino , Masculino , Ratones , NataciónRESUMEN
There is strong evidence linking inherited long QT syndromes with an increased risk of drowning due to fatal arrhythmias in the water. Drug-induced long QT syndrome (DILQTS) is hypothesized to increase the risk of drowning by similar mechanisms. It is suggested that QT prolongation caused by a drug or drugs, when combined with the autonomic conflict associated with the mammalian dive reflex and/or the cold shock reflex, sets up conditions that may result in a sudden fatal arrhythmia while in water - thus an increased risk of drowning related to a drug-induced prolongation of the QT interval. Many widely used drugs prolong the QT interval thus raising a drug safety issue that needs confirmation or refutation.
Asunto(s)
Ahogamiento/etiología , Síndrome de QT Prolongado/inducido químicamente , Síndrome de QT Prolongado/complicaciones , Consumo de Bebidas Alcohólicas/efectos adversos , Citalopram/toxicidad , Reflejo de Inmersión/fisiología , Ahogamiento/fisiopatología , Humanos , Síndrome de QT Prolongado/fisiopatología , Metanfetamina/toxicidad , Modelos Biológicos , Factores de Riesgo , Trastornos Relacionados con Sustancias/complicacionesRESUMEN
The whale shark (Rhincodon typus) is a wide-ranging, filter-feeding species typically observed at or near the surface. This shark's sub-surface habits and behaviors have only begun to be revealed in recent years through the use of archival and satellite tagging technology. We attached pop-up satellite archival transmitting tags to 35 whale sharks in the southeastern Gulf of Mexico off the Yucatan Peninsula from 2003-2012 and three tags to whale sharks in the northeastern Gulf off Florida in 2010, to examine these sharks' long-term movement patterns and gain insight into the underlying factors influencing their vertical habitat selection. Archived data were received from 31 tags deployed on sharks of both sexes with total lengths of 5.5-9 m. Nine of these tags were physically recovered facilitating a detailed long-term view into the sharks' vertical movements. Whale sharks feeding inshore on fish eggs off the northeast Yucatan Peninsula demonstrated reverse diel vertical migration, with extended periods of surface swimming beginning at sunrise followed by an abrupt change in the mid-afternoon to regular vertical oscillations, a pattern that continued overnight. When in oceanic waters, sharks spent about 95% of their time within epipelagic depths (<200 m) but regularly undertook very deep ("extreme") dives (>500 m) that largely occurred during daytime or twilight hours (max. depth recorded 1,928 m), had V-shaped depth-time profiles, and comprised more rapid descents (0.68 m sec-1) than ascents (0.50 m sec-1). Nearly half of these extreme dives had descent profiles with brief but conspicuous changes in vertical direction at a mean depth of 475 m. We hypothesize these stutter steps represent foraging events within the deep scattering layer, however, the extreme dives may have additional functions. Overall, our results demonstrate complex and dynamic patterns of habitat utilization for R. typus that appear to be in response to changing biotic and abiotic conditions influencing the distribution and abundance of their prey.